Method of manufacturing a semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device, comprises the steps of: forming a first insulating film on a first substrate; forming a second insulating film on the first insulating film; forming an amorphous silicon film on the second insulating film; holding a metal element that promotes the crystallization of silicon in contact with a surface of the amorphous silicon film; crystallizing the amorphous silicon film through a heat treatment to obtain a crystalline silicon film; forming a thin-film transistor using the crystalline silicon film; forming a sealing layer that seals the thin-film transistor; bonding a second substrate having a translucent property to the sealing layer; and removing the first insulating film to peel off the first substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/504,235, filed Feb. 15, 2000, which is a continuation of U.S.application Ser. No. 09/013,960, filed Jan. 27, 1998, now U.S. Pat. No.6,998,282, which is a continuation of U.S. application Ser. No.08/602,324, filed Feb. 16, 1996, now U.S. Pat. No. 5,821,138, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 07-053219 on Feb. 16, 1995, all of which are incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique by which a display panelwhich is flexible (having a flexibility) is provided, and moreparticularly to a technique by which a flexible active matrixliquid-crystal display unit is provided.

2. Description of the Related Art

There has been known a liquid-crystal display unit as a display unitwhich is small-sized, light in weight and of the thin type. This has astructure in which liquid crystal is interposed between a pair oftranslucent substrates which are bonded to each other at intervals ofseveral μm and held in this state as the structure of a display panel.In the operation of the display unit, an electric field is applied toliquid crystal in a predetermined region so as to change its opticalcharacteristics, whereby the presence/absence of a light transmittedthrough a panel and the amount of transmitted light are controlled.

As a technique by which the display characteristics of thisliquid-crystal display unit is further enhanced, there has been knownthe active matrix display panel. This is to arrange switching thin-filmtransistors (in general, an amorphous silicon thin film is used) in therespective pixels disposed in the form of a matrix, and to controlcharges that takes in or out of the respective pixels by the thin-filmtransistors.

In order to improve the characteristics of the active matrixliquid-crystal display device, it is necessary to improve thecharacteristics of the thin-film transistor as used. However, under theexisting circumstance, it is difficult to improve such characteristicsin view of the relationship of the substrate as used.

What is required for the substrate used in the liquid-crystal displaypanel is such an optical characteristic that the substrate transmits avisible light. Substrates having such an optical characteristic are of avariety of resin substrates, a glass substrate, a quartz substrate, etc.Of them, the resin substrate is low in a heat-resistance, and thereforeit is hard to manufacture the thin-film transistor on its surface. Also,the quartz substrate can withstand a high temperature of 1000° C. ormore, however, it is expensive and causes an economical problem when thedisplay unit is enlarged. For that reason, the glass substrate isgenerally used.

In order to improve the characteristics of the thin-film transistor, asilicon semiconductor thin film having a crystalline property need beused for the thin-film semiconductor that forms the thin-filmtransistor. However, in order to form the crystalline silicon thin film,a sample must be exposed to a high-temperature atmosphere, and in thecase of using the glass substrate, there arises such a problem that thesubstrate is warped or deformed. In particular, when making thesubstrate large in area, that problem becomes remarkable.

As a technique by which a liquid-crystal display panel that solves sucha problem and has a high display characteristic is obtained, there hasbeen known a technique disclosed in Japanese Patent UnexaminedPublication No. Hei 6-504139. This technique is that a thin-filmtransistor is manufactured by using a monocrystal silicon thin filmformed through the SOI technique, etc., that thin-film transistor ispeeled off from the substrate for an epitaxial growth, and the thin-filmtransistor is bonded to an arbitrary substrate having an opticalcharacteristic as required, to thereby obtain a panel constituting aliquid-crystal display unit.

In the case of using this technique, since the monocrystal silicon thinfilm formed using a known SOI technique can be used, a thin-filmtransistor having a high characteristic can be obtained. Also, asubstrate having a curved surface can be used.

In the technique disclosed in Japanese Patent Unexamined Publication No.Hei 6-504139, a thin-film transistor is manufactured using the SOItechnique. However, in the SOI technique under the existingcircumstance, it is difficult to form a monocrystal thin film in a largearea of 10 inch diagonal or more.

For example, under the existing circumstance, the maximum monocrystalwafer is of 16 inches in size. In this case, the maximum square panel asobtained is of 16×(½)⁻²≈11 inch diagonal.

On the other hand, it is expected that the liquid-crystal display panelas required is of 20 or 30 inches or more in the diagonal dimension inthe future. It is impossible to constitute such a large-sizedliquid-crystal display panel through the method using the known SOItechnique.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an objectof the present invention is to provide a technique by which a thin-filmtransistor having a high characteristic over a large area ismanufactured.

Another object of the present invention is to provide a technique bywhich a display panel is obtained using that technique.

Still another object of the present invention is to provide a thin-filmtransistor and a display panel which are manufactured using theabove-mentioned techniques.

In order to solve the above-mentioned problems, one aspect of thepresent invention has been achieved by the provision of a method ofmanufacturing a semiconductor device, which comprising the steps of:

forming a first insulating film on a first substrate;

forming a second insulating film on the first insulating film;

forming an amorphous silicon film on said second insulating film;

holding a metal element that promotes the crystallization of silicon incontact with a surface of said amorphous silicon film;

crystallizing said amorphous silicon film through a heat treatment toobtain a crystalline silicon film;

forming a thin-film transistor using said crystalline silicon film;

forming a sealing layer that seals said thin-film transistor;

bonding a second substrate having a translucent property to said sealinglayer; and

removing said first insulating film to peel off said first substrate.

A specified example of the above-mentioned structure is shown in FIGS. 1to 3. First, in FIG. 1, a first insulating film (silicon oxide film) 102that functions as a peeling layer is formed on a glass substrate 101which forms a first substrate. Then, a silicon oxide film 103 is formedas a second insulating film. The silicon oxide films 102 and 103 aremanufactured by different methods, respectively, and the first siliconoxide film 102 is made of a material which is readily removed by etchingat a poststage.

Subsequently, an amorphous silicon film 104 is formed on a secondinsulating film 103. Then, a solvent containing a metal element thatpromotes the crystallization of silicon therein is coated on theamorphous silicon film 104, to thereby form a water film 105, and a spindry process is conducted using a spinner 106 into a state in which themetal element is brought in contact with the surface of the amorphoussilicon film 104.

Thereafter, a crystal silicon film 107 is obtained by conducting a heattreatment, and the crystalline silicon film 107 is formed into an activelayer 108, to thereby form a thin-film transistor as shown in FIGS. 2Aand 2B. After the formation of the thin-film transistor, a layer 119 forsealing the thin-film transistor is formed. Then, a flexible translucentsubstrate 120 is bonded onto the layer 119. Thereafter, the siliconoxide film which is of the first insulating film 102 forming a peelinglayer is removed by conducting an etching process so that the glasssubstrate 101 is peeled off from the thin-film transistor.

Another aspect of the present invention has been achieved by theprovision of a method of manufacturing a semiconductor device, whichcomprises the steps of:

forming a first insulating film on a first substrate having a grooveformed in a surface thereof;

forming a second insulating film on said first insulating film;

forming an amorphous silicon film on said second insulating film;

holding a metal element that promotes the crystallization of silicon incontact with a surface of said amorphous silicon film;

crystallizing said amorphous silicon film through a heat treatment toobtain a crystalline silicon film;

forming a thin-film transistor using said crystalline silicon film;

forming a sealing layer that seals said thin-film transistor;

bonding a second substrate having a translucent property to said sealinglayer; and

removing said first insulating film by using an etching solvent to peeloff said first substrate.

Still another aspect of the present invention has been achieved by theprovision of a method of manufacturing a semiconductor device, whichcomprises the steps of:

forming a first insulating film on a first substrate having a grooveformed in a surface thereof;

forming a second insulating film on said first insulating film;

forming an amorphous silicon film on said second insulating film;

holding a metal element that promotes the crystallization of silicon incontact with a surface of said amorphous silicon film;

crystallizing said amorphous silicon film through a heat treatment toobtain a crystalline silicon film;

forming a thin-film transistor using said crystalline silicon film;

forming a sealing layer that seals said thin-film transistor;

bonding a second substrate having a translucent property to said sealinglayer; and

removing said first insulating film by using an etching solvent to peeloff said first substrate;

wherein a gap is defined between a bottom portion of said groove andsaid insulating film, and said etching solvent enters said gap.

In the structures described in this specification, one kind or pluralkinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cuand Au can be used for the metal element that promotes thecrystallization of silicon. In particular, Ni can obtain the higherreproducibility and effects.

Also, the metal element that promotes the crystallization of silicon isso adjusted as to provide a density of 1×10¹⁴ to 5×10¹⁸ atm cm⁻³ in thesilicon film. This is because the density of 1×10¹⁴ atms cm⁻³ isrequired for crystallization, and the density of more than 5×10¹⁸ atmcm⁻³ causes the semiconductor characteristic to be lowered. It should benoted that the density of atoms is defined as a minimum value of valuesmeasured by using SIMS (secondary ion mass spectroscopy) in thisspecification.

The crystalline silicon film obtained by using the above-mentioned metalelement contains hydrogen and/or halogen at the density of 0.0005 to 5atms % for neutralization of an unpaired coupling therein. Examples ofthe halogen are chlorine, fluorine and bromine.

Yet still another aspect of the present invention has been achieved bythe provision of a method of manufacturing a semiconductor device, whichcomprises the steps of:

forming a first insulating film on a first substrate;

forming a second insulating film on said first insulating film;

forming an amorphous silicon film on said second insulating film;

holding a metal element that promotes the crystallization of silicon incontact with a surface of said amorphous silicon film;

irradiating a laser beam onto said amorphous silicon film to change aregion on which the laser beam is irradiated into a monocrystal-likeregion or substantially monocrystal-like region;

forming a thin-film transistor by using the monocrystal-like region orsubstantially monocrystal-like region as an active layer;

forming a sealing layer that seals said thin-film transistor;

bonding a second substrate having a translucent property to said sealinglayer; and

removing said first insulating film to peel off said first substrate.

In the above-mentioned structure, the monocrystal-like region orsubstantially monocrystal-like region contains substantially no grainboundary therein, contains hydrogen and/or halogen atoms forcompensating a defect at a density of 1×10¹⁵ to 1×10²⁰ atms cm⁻³therein, also contains carbon and nitrogen atoms at a density of 1×10¹⁶to 5×10¹⁸ atms cm⁻³, and further contains oxygen atoms at a density of1×10¹⁷ to 5×10¹⁹ atms cm⁻³.

Yet still another aspect of the present invention has been achieved bythe provision of a method of manufacturing a semiconductor device,comprising the steps of:

forming a first insulating film on a first substrate;

forming a second insulating film on said first insulating film;

forming an amorphous silicon film on said second insulating film;

holding a metal element that promotes the crystallization of silicon incontact with a surface of said amorphous silicon film;

irradiating a laser beam onto said amorphous silicon film to change aregion on which the laser beam is irradiated into a region having acrystalline property;

forming a thin-film transistor by using the region having thecrystalline property as an active layer;

forming a sealing layer that seals said thin-film transistor;

bonding a second substrate having a translucent property to said sealinglayer; and

removing said first insulating film to peel off said first substrate.

In a method of introducing the metal element that promotes thecrystallization of silicon in accordance with the present inventiondescribed in this specification, it is simple to use a solventcontaining the metal element therein. For example, in the case of usingNi, at least one kind of compound selected from nickel bromide solvent,nickel acetate solvent, nickel oxalate solvent, nickel carbonatesolvent, nickel chloride solvent, nickel iodide solvent, nickel nitratesolvent, nickel sulfate solvent, nickel formate solvent, nickelacetylacenate solvent, nickel 4-cyclohexyl butyrate solvent, nickel2-ethyl hexanoic acid solvent, nickel oxide solvent, and nickelhydroxide solvent can be used.

In the case of using Fe (iron) as the metal element, a material known asion salt, for example, an Fe compound selected from bromide (FeBr₂6H₂O),iron (II) bromide (FeBr₃6H₂O), iron (II) acetate (Fe(C₂H₃O₂)₃xH₂O), iron(I) chloride (FeCl₂4H₂O), iron (II) chloride (FeCl₃6H₂O), iron (II)fluoride (FeF₃3H₂O), iron (II) nitrate-(Fe(NO₃)9H₂O), iron (I)phosphorate (Fe₃(PO₄)₂8H₂O), and iron (II) phosphorate (FePO₄2H₂O) canbe used.

In the case of using Co (cobalt) as the metal element, a material knownas a cobalt salt, a Co compound selected from a material known as acobalt salt, for example, cobalt bromide (CoBr₆H₂O), cobalt acetate(Co(C₂H₃O₂)₂4H₂O), cobalt chloride (CoCl₂6H₂O), cobalt fluoride(CoF₂xH₂O), and cobalt nitrate (Co(NO₃)₂6H₂O) can be used.

In the case of using Ru (ruthenium) as the metal element, as a rutheniumcompound, a material known as ruthenium salt, for example, rutheniumchloride (RuCl₃H₂O) can be used.

In the case of using Rh (rhodium) as the metal compound, as a rhodiumcompound, a material known as rhodium salt, for example, rhodiumchloride (RhCl₃3H₂O) can be used.

In the case of using Pd (palladium) as the metal element, as a palladiumcompound, a material known as palladium salt, for example, palladiumchloride (PdCl₂2H₂O) can be used.

In the case of using Os (osmium) as the metal element, as an osmiumcompound, a material known as osmium salt, for example, osmium chloride(OsCl₃) can be used.

In the case of using Ir (iridium) as the metal element, as an iridiumcompound, a material known as iridium salt, for example, a materialselected from iridium trichloride (IrCl₃3H₂O) and indium tetrachloride(IrCl₄) can be used.

In the case of using Pt (platinum) as the metal element, as a platinumcompound, a material known as platinum salt, for example, platinum (II)chloride (PtCl₄5H₂O) can be used.

In the case of using Cu (copper) as the metal element, as a coppercompound, a material selected from copper (II) acetate (Cu(CH₃COO)₂),copper (II) chloride (CuCl₂2H₂O) and copper (II) nitrate (Cu(NO₃)₂3H₂O)can be used.

In the case of using gold as the metal element, as a gold compound, amaterial selected from gold trichloride (AuCl₃xh₂O) and gold nitride(AuHCl₄4H₂O) can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate (an) embodiment(s) of theinvention and, together with the description, serve to explain theobjects, advantages and principles of the invention. In the drawings,

FIGS. 1A to 1D are diagrams showing a process of manufacturing aliquid-crystal panel in accordance with an embodiment of the presentinvention;

FIGS. 2A to 2C are diagrams showing a process of manufacturing aliquid-crystal panel in accordance with an embodiment of the presentinvention;

FIGS. 3A and 3B are diagrams showing a process of manufacturing aliquid-crystal panel in accordance with an embodiment of the presentinvention;

FIG. 4 is a diagram showing a liquid-crystal panel in accordance with anembodiment of the present invention;

FIGS. 5A to 5D are diagrams showing a process of manufacturing aliquid-crystal panel in accordance with an embodiment of the presentinvention;

FIG. 6 is a diagram showing an outline of a pixel region of aliquid-crystal display unit;

FIG. 7 is a diagram showing a state in which an oxide film is formed ona substrate having concave and convex formed on a surface thereof;

FIG. 8 is a diagram showing a state in which a liquid-crystal displayunit is disposed in a helmet; and

FIG. 9 is a diagram showing a state in which a liquid-crystal displayunit is disposed in a front glass of a vehicle; and

FIG. 10 is a diagram showing a state in which a liquid-crystal displayunit is disposed in a front glass of a cockpit of an airplane.

FIGS. 11(A) to 11(F) show a manufacturing process for a liquid crystalpanel in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of embodiments inaccordance with the present invention with reference to the accompanyingdrawings.

First Embodiment

A first embodiment relates to an example in which a liquid-crystaldisplay thin-film integrated circuit having a large area which has beenfabricated on a glass substrate at a low-temperature process of 550° C.or lower is transferred from the glass substrate onto a PET(polyethylene terephthalate) which is of a flexible substrate toconstitute an active matrix liquid-crystal display unit which can bedisposed even on a curved surface. More particularly, in thisembodiment, the structure of a pixel region will be described. In thisdescription, a liquid-crystal display unit is shown as one example,however, a technique described in this specification is available to theEL-type display unit.

First, a glass substrate 101 is prepared. Fine concave portions havebeen formed on a surface of the glass substrate 101 in advance. In thisexample, the concave portions are several thousands Å to several μm inwidth and height, several to several tens μm in depth, and shaped in theform of a lattice or stripe. It is preferable to make the concaveportions deep in a range in which the flatness of a peeling layer 102formed later is maintained. A method of forming the concave portions maybe achieved through an etching process using a photolithography processor a mechanical etching process.

A silicon oxide film that functions as the peeling layer 102 is formedon the glass substrate 101. In this example, the silicon oxide filmusing a silicon oxide base coating formation coating solution isutilized. The silicon oxide base coating formation coating solution isof silanol base monomer, oligomer, etc., being resolved in an organicsolvent such as alcohol or ketone, or of fine particles of silicon oxidebeing dispersed in an organic solvent. As a specific example of such asilicon oxide base coating formation coating solution, OCD (ohkadiffusion source) made by Tokyo Ohka Kogyo Kabushiki Kaisha can be used.

The above-mentioned OCD solution is coated on a surface to be formed byusing a spinner, etc., and baked at a temperature of 200 to 300° C.,thereby being capable of simply forming the silicon oxide film. Also,the silicon oxide film formed by using those silicon oxide base coatingformation coating solutions (not limited to OCD) has such acharacteristic that its etching rate is remarkably high (high by onefigure or more depending on the conditions) in comparison with thesilicon oxide film formed through the sputtering technique or the CVDtechnique. For example, according to an experiment conducted by thisinventors, the etching rate of an oxide film (used for a gate insulatingfilm or an interlayer insulating film) formed through the plasma CVDtechnique using a TEOS gas to buffer hydrofluoric acid is about 1000 to2000 Å/min, whereas the etching rate of a silicon oxide film formed byusing the above-mentioned OCD solution to buffer hydrofluoric acid is 1μm/min or longer.

In this embodiment, the peeling layer is formed in the OCD solution madeby Tokyo Ohka Kogyo Kabushiki Kaisha by using Type 2 Si 59000. Theformation of the peeling layer is performed by coating theabove-mentioned OCD solution by a spinner and baking at a temperature of250° C. for 30 minutes. In this example, the peeling layer 102 which ismade of the silicon oxide film is 1 μm in thickness. It should be notedthat attention must be paid so that the surface of the peeling layerbecomes flattened.

Gaps 701 are defined between the peeling layer 102 and the glasssubstrate 101 by the concave and convex of the glass substrate 101 asshown in FIG. 7. Also, it is effective to adjust the density of the OCDsolution so as to form the gaps 701.

After the peeling layer 102 has been formed, a silicon oxide film 103that forms an under layer is formed. The silicon oxide film 103 isformed with a fine film quality through the plasma CVD technique usingthe TEOS gas. Since the silicon oxide film 103 functions as a protectivefilm that covers a back side of the thin-film transistor later, itsthickness must be set to 5000 Å or more. Also, the formation of thesilicon oxide film 103 that forms an under layer may be conductedthrough the sputtering technique (FIG. 1A).

Subsequently, an amorphous silicon film 104 shown in FIG. 1B is formedthrough the plasma CVD technique or the decompression thermal CVDtechnique. The formation of the amorphous silicon film 104 may beperformed by using a conventionally known film forming method. Theamorphous silicon film 104 may be about 500 Å in thickness. Furthermore,a sample is disposed on a spinner 106, and a nickel acetate solutionadjusted to a predetermined density is coated thereon to form a waterfilm 105. Then, an unnecessary solution is blown off by conducting thespin dry using the spinner 106, resulting in a state where the nickelelement is held in contact with the surface of the amorphous siliconfilm 104.

The amorphous silicon film 104 is crystallized by conducting a heattreatment in that state. The heat treatment may be conducted at atemperature of 550° C. for 4 hours. Even though the amorphous siliconfilm is subjected to the heat treatment at a temperature of 550° C.,crystallization does not usually progress without the addition of aprocess for several hundreds hours or longer. However, the crystallinesilicon film can be obtained even in the above-mentioned condition byusing a certain metal element (in this example, nickel element) thatpromotes the crystallization of silicon. Also, in the case of using sucha metal element, the crystalline silicon film can be obtained if heatingis conducted for several tens hours even at a temperature of about 500°C. likewise. The effect of such a low-temperature crystallization can beremarkably obtained when nickel is used as a metal element. A substratewhich is inexpensive and an area of which can be readily increased suchas a Corning 7059 glass substrate can be used if an applied temperatureis about 550° C. in a process of crystallizing the amorphous siliconfilm 104 through the heat treatment. Hence, a crystalline silicon filmof a large area can be obtained with restraining the production costs.

In this manner, a crystalline silicon film 107 is obtained as shown inFIG. 1C. The crystallization of the silicon film 107 is further improvedby the irradiation of a laser beam. Then, the surface of the crystallinesilicon film 107 is etched by about 100 Å. This is to remove the nickellayer (perhaps, being changed into nickel silicide) of a high densitywhich exists on the surface of the crystalline silicon film 107. Then,an active layer 108 of the thin-film transistor is obtained bypatterning the crystalline silicon film 107, as shown in FIG. 1D.

Subsequently, a silicon oxide film that covers the active layer 108 andfunctions as a gate insulating film 109 is formed as shown in FIG. 2A.The gate insulating film 109 may be set to about 1000 Å in thickness.The thickness of the gate insulating film 109, etc., are determined inaccordance with a required characteristic or a utilized process.

After the gate insulating film 109 has been formed, a film that mainlycontains aluminum with a small amount of scandium is formed, andpatterned, to thereby obtain a gate electrode 110. The film mainlycontaining aluminum may be, for example, 6000 Å in thickness. In thiscase, the thickness of the gate electrode 110 is 6000 Å.

Furthermore, anodic oxidation is conducted with a gate electrode 110 asan anode in an electrolyte, to thereby form an anode oxide layer 111 of2000 Å thickness. With this thickness of the anode oxide film 111, anoffset gate region can be formed in a process of implanting impurityions later.

After the formation of the anodic oxidation layer 111, impurity ions areimplanted for forming the source and drain regions. In this example, inorder to obtain the n-channel thin-film transistor, P (phosphorus) ionsare implanted. This process may be conducted through the plasma dopingtechnique or the ion implanting technique.

Through this process, a source region 112, drain region 115, a channelformation region 114, and an offset gate region 113 are formed in aself-matching manner. Also, after the implantation of impurity ions hasbeen finished, a laser beam or an intense light beam is irradiatedthereonto to conduct the recrystallization of the source and drainregions 112 and 115 and the activation of implanted ions. In thismanner, a state shown in FIG. 2A is obtained.

After the state shown in FIG. 2A is obtained, a silicon oxide film isformed as an interlayer insulating film 116. The interlayer insulatingfilm 116 may be made of an organic resin. The organic resin may be of anepoxy resin, an acrylate resin, a polyimide resin, etc. Also, theinterlayer insulating film 116 may be of a multi-layer structureconsisting of two or more layers of a variety of resin materials, or alaminated structure consisting of a silicon oxide film and a resinlayer.

After the formation of the interlayer insulating film 116, contact holesare formed. Then, a source electrode 117 is formed using a laminatedbody consisting of titan and aluminum. Furthermore, a second interlayerinsulating film 200 that consists of a silicon oxide film is formedthereon. Subsequently, an electrode 118 connected to a drain region isformed using ITO. This electrode 118 constitutes a pixel electrodeconnected to the drain region of the thin-film transistor. In thismanner, the thin-film transistor including even a wire has beencompleted (FIG. 2B).

As shown in FIG. 2C, a resin material 119 that functions as a sealingmaterial for sealing the thin-film transistor including even a wire isformed. The resin material 119 may be of an epoxy resin, an acrylateresin, a polyimide resin, etc. Also, the resin material 119 may be of amulti-layer structure consisting of two or more layers of a variety ofresin materials.

In this example, the resin material 119 is of an epoxy resin thatfunctions as an adhesive of the UV curing type. Then, a translucent andflexible resin substrate 120 that forms a liquid-crystal panel substrateis bonded with the resin material 119. In this example, the resinsubstrate 120 is of a PET (polyethylene terephthalate) film having athickness of 1 mm. Also, the method of bonding the resin substrate 120may be made by using an adhesive layer instead of the resin material119.

Then, as shown in FIG. 3A, a peeling layer is etched by using a bufferhydrofluoric acid. In this process, since grooves are defined in thesurface of the glass substrate 101, gaps exist between the peeling layer102 and the surface of the glass substrate 101 due to the existence ofthe grooves. Then, an etchant enters those gaps, whereby etchingprogresses rapidly. Furthermore, the silicon oxide film formed using asilicon oxide base coating formation coating solution which isrepresented by an OCD solution is higher in etching rate by one figureor more in comparison with the silicon oxide film formed through theplasma CVD technique or sputtering technique. Hence, in this etchingprocess, only the peeling layer 102 can be selectively removed.

As a result, as shown in FIG. 3A, the glass substrate 101 and thesilicon oxide film 103 that forms an under layer are peeled off fromeach other.

In this way, a state shown in FIG. 3B is obtained. In this state, one ofthe active matrix liquid-crystal display panels has been completed. Inother words, one of liquid-crystal panels with a structure in whichliquid crystal is interposed and held between a pair of substrates hasbeen completed.

It should be noted that in one panel shown in FIG. 3B, only a part ofone pixel in a pixel region is shown. However, the peripheral circuitthin-film transistor is constituted and the peripheral drive circuitsare integrally formed with other circuits through the same process asthat described above.

Further, an opposing electrode 123 and an orientation film 122 aredisposed on the surface of a PET film 124 having a thickness of 1 mm.Thus, a panel which is paired with the panel shown in FIG. 3B isobtained. Then, an orientation film 121 for orienting liquid crystal isformed on the silicon oxide film 103 exposed from the panel shown inFIG. 3B. Two panels are bonded to each other, and a TN-type liquidcrystal is implanted in a gap (5 μm) therebetween. Thus, theliquid-crystal display panel shown in FIG. 4 is completed. Also, as notshown in the figure, a color filter, a phase compensation film, and apolarization film are disposed as occasion demands.

In this embodiment, the TN liquid crystal into which the UV curing resinmaterial is mixed is used. After the completion of the panel,ultraviolet rays are irradiated onto the resin material to cure theresin material. As a result, an interval between a pair of panels isheld by the resin material which has been cured in the form of a column.Also, since the interval between those two panels cannot be held by onlythat resin material when bonding those panels, it is necessary to useknown spacers.

Also, in a state shown in FIG. 4, since there is a possibility that thedeterioration of the characteristics progresses by entering of water,etc., the entire panel is sealed with a thermosetting resin film.

In the structure shown in FIG. 4, since a resin substrate having aflexibility as a substrate is used, the entire liquid-crystal panel canprovide the flexibility. Also, because of the active matrixliquid-crystal display unit which is formed by thin-film transistorsusing a crystalline silicon film, it can provide a high image displayfunction.

Second Embodiment

A second embodiment is an example in which Cu (copper) is used as ametal element that promotes the crystallization of silicon in theprocess described with reference to the first embodiment. In thisembodiment, copper elements are introduced using copper (II) acetate(Cu(CH₃COO)₂) solution. The density of the copper elements in thatsolution is adjusted so that the density of copper elements that remainin a final silicon film is set to 1×10¹⁶ to 5×10¹⁹ atms cm⁻³.

In the case of using Cu as the metal element that promotes thecrystallization of silicon, a heat treatment for crystallization isconducted under a condition of 580° C. and 4 hours. This is because Cuis slightly small in function that promotes the crystallization ofsilicon in comparison with Ni. Other structures and process conditionsare the same as those shown in the first embodiment.

Third Embodiment

A third embodiment shows an example in which a silicon film having amonocrystal-like region or substantially monocrystal-like region isformed on a glass substrate, and the active matrix liquid-crystaldisplay unit having a flexible structure is constituted using thissilicon film.

In this example, a Corning 7059 glass substrate (warp point 593° C.) isused as a glass substrate 501. Lattice-like or stripe-like grooves whichare several μm in width and several to several tens μm in depth havebeen formed in advance.

First, a peeling layer 502 is formed on a glass substrate 501. Thepeeling layer 502 is of a silicon oxide film using the above-mentionedOCD solution. In this situation, fine gaps are formed on the bottomportion of the grooves because of the existence of the above-mentionedgrooves.

Then, a silicon oxide film 503 is formed on the peeling layer 502through the plasma CVD technique using the TEOS gas. Since the siliconoxide film 503 serves as a support that supports the thin-filmtransistor circuit later, it is thickened. In this example, the siliconoxide film 503 is formed to provide a thickness of 8000 Å. Further, anamorphous silicon film 504 having a thickness of 300 Å is formed throughthe plasma CVD technique or the decompression thermal CVD technique.

Subsequently, a sample is disposed on a spinner 506, and a nickelacetate solution is coated thereon to form a water film 505. The contentdensity of nickel elements in the nickel acetate solution to be coatedis adjusted so that the density of nickel elements that remain in thesilicon film is finally 1×10¹⁶ to 5×10¹⁹ atms cm⁻³. The density ofnickel elements in the silicon film is defined by the maximum value of asilicon value using SIMS (secondary ion mass spectrometry).

After a water film 505 of the nickel acetate solution has been formed,an unnecessary solution is blown off by conducting the spin dry. In thisway, the nickel element is held in contact with the surface of theamorphous silicon film 504. The amorphous silicon film 504 iscrystallized by the irradiation of a laser beam in that state. In thisexample, a KrF excimer laser which has been beam-processed in a linearshape is used. In the irradiation of the laser beam, the sample isheated at a temperature of 550° C.

The laser beam used here is of a beam which has been processed throughan optical system (which is constituted by a lot of various lenses) soas to be in a linear shape which is several tens cm in length and about1 mm in width. The crystallization of a silicon film using the linearlaser beam allows a region which has been crystallized as indicated byreference numeral 507 in FIG. 5B to grow bits by bits, by irradiation ofthe laser beam onto the amorphous silicon film 504 while slowly scanningthe film 504 by the laser beam.

A region 507 which has been crystallized by the irradiation of the laserbeam has monocrystal-like or substantially monocrystal-like electriccharacteristics. In other words, it has a crystal structure where nograin boundary substantially exists in that region 507. However,different from a general monocrystal wafer, hydrogen and/or halogenelements for compensating a defect, having a density of 1×10¹⁵ to 1×10²⁰atms cm⁻³ is contained in that region 507. This is because the startingfilm is of an amorphous silicon film.

Also, the amorphous silicon film contains carbon and nitrogen atoms at adensity of 1×10¹⁶ to 5×10¹⁸ atms cm⁻³ therein Also, it contains oxygenatoms at a density of 1×10¹⁷ to 5×10¹⁹ atms cm⁻³. That the amorphoussilicon film contains carbon, nitrogen and oxygen results from thestarting film being of the amorphous silicon film 504 which has beenformed through the CVD technique. In other words, this is becausecarbon, nitrogen and oxygen are unavoidably contained in the amorphoussilicon film 504 which has been formed through the plasma CVD techniqueor the decompression thermal CVD technique.

Also, in the case of using the metal element that promotes thecrystallization of silicon as described in this embodiment, the metalelement having a density of 1×10¹⁶ to 5×10¹⁹ atms cm⁻³ is containedtherein. This density range means that the metal characteristics areexhibited in a range more than the above range, and an action forpromoting the crystallization of silicon cannot be obtained in a rangeless than the above range.

Also, the monocrystal-like region or substantially monocrystal-likeregion which is obtained by the crystallization due to the irradiationof a laser beam as described in this embodiment can be obtained as aslender region 507, but its width cannot be enlarged so much. In otherwords, to obtain the above-mentioned region over a large area isimpossible under the existing circumstance.

However, in the active matrix liquid-crystal display unit, since thethin-film transistors are aligned regularly in columns as shown in FIG.6, what is actually required for crystallization is of a specifiedlinear region.

In FIG. 6, reference numeral 601 denotes a source line, and referencenumeral 602 is a gate line. Also, reference numeral 603 is an ITOelectrode that constitutes a pixel electrode. Also, reference numeral605 denotes a contact on the source region of the thin-film transistor,604 is a contact on the gate electrode thereof, and 606 is a contact onthe drain region and the pixel electrode 603.

In the structure shown in FIG. 6, a region indicated by referencenumeral 607 is of a region that constitutes an active layer of thethin-film transistor. Hence, it is sufficient to crystallize at leastthis region.

Actually, the structure shown in FIG. 6 is formed in the form of amatrix of several hundreds×several hundreds. Accordingly, what isrequired at the minimum is that the linear regions indicated byreference numerals 608 and 609 may be crystallized. Since the width ofthe active layer is about several to several tens μm, the linear regionsindicated by reference numerals 608 and 609 can be changed into themonocrystal-like region or substantially monocrystal-like region by theirradiation of a laser beam as described in this embodiment.

In this embodiment, the monocrystal-like region or substantiallymonocrystal-like region is selectively formed as indicated by referencenumeral 507, by irradiating a linear laser beam in a scanning manner asshown in FIG. 5B.

In this embodiment, the metal element that promotes the crystallizationof silicon is used. However, in the case of using no metal element, itis hard to form the monocrystal-like region or substantiallymonocrystal-like region.

Also, since the irradiation conditions of a laser beam are very fine, itis necessary that preliminary experiments are sufficiently conducted soas to find out its conditions. What is particularly important in theirradiation conditions of a laser beam is a relationship between theirradiation density of a laser beam and its scanning speed.

Even when the metal element is used, it is hard to form themonocrystal-like region or substantially monocrystal-like region withoutheating when the laser beam is irradiated. In this example, the heattemperature is set to 550° C., but it is preferable to increase thetemperature as high as possible in a range of temperature to which theglass substrate is resistant. Specifically, it is desirable to increasethe temperature as high as possible to an extent less than a warp pointof the glass substrate.

The monocrystal-like region or substantially monocrystal-like regionobtained by the method shown in FIG. 5B is of a linear shape having alongitudinal direction toward a depthwise of FIG. 5B. Then, thethin-film transistors to be formed are so disposed as to be aligned in alot of numbers toward the depthwise of the figure.

In a process of irradiating a laser beam shown in FIG. 5B, themonocrystal-like region or substantially monocrystal-like region hasbeen formed, an active layer 508 of the thin-film transistor is formedas shown in FIG. 5C by conducting a patterning. The like active layersare formed in a lot of numbers simultaneously at a back side and a frontside of the active layer 508 with respect to the paper.

The active layers 508 are formed of the monocrystal-like region orsubstantially monocrystal-like region. In other words, no grain boundarysubstantially exists in the active layer. Hence, the active layers 508can provide electric characteristics equal to that of a transistorconstituted using a monocrystal wafer or a thin-film transistorconstituted using a monocrystal silicon thin film obtained through theSOI technique, etc.

After the formation of the active layers 508, a silicon oxide film 509that functions as a gate insulating film is formed through the plasmaCVD technique or the decompression thermal CVD technique. The thicknessof the silicon oxide film is set to 1200 Å. Further, a gate electrode510 that mainly contains aluminum is formed. An oxide layer 511 isformed by anodic oxidation in the periphery of that gate electrode 510.

The portion of an active layer 508 indicated by a state shown in FIG. 5Cis of a portion of the channel formation region. What is shown in FIG.5C is a cross-section of the thin-film transistor shown in FIG. 2,viewed at an angle different by 90°. The section shown in FIG. 5Ccorresponds to a section taken along the line A-A′ of FIG. 6.

After the formation of an anodic oxide 511, an interlayer insulatingfilm 512 is formed on the anodic oxide 511 through the plasma CVDtechnique using a TEOS gas. Further, after contact holes have beenformed, a contact wire (contact electrode) 513 to the gate electrode 510is formed thereon. In this situation, although not shown, requiredwiring are simultaneously conducted.

Then, an adhesive layer 515 made of an epoxy resin or the like, whichalso functions as a sealing material, is formed thereon, to thereby sealthe wiring and the circuits which have been previously formed. Theadhesive layer 515 is of the type which is cured by the irradiation ofUV rays. Then, a translucent substrate 515 formed of a PET film isbonded onto an adhesive layer 514.

The peeling layer 502 is removed using a hydrofluoric acid base etchant(for example buffer hydrofluoric acid). In this situation, the etchantenters grooves defined in the glass substrate 501, thereby facilitatingthe etching of the peeling layer 502. Thus, the glass substrate 501 canbe peeled off.

With the peeling off of the glass substrate 501, a state shown in FIG.5D is obtained. In this way, one of panels that constitute the activematrix liquid crystal display unit is completed. Thereafter, an opposingpanel is fabricated as described with reference to the first embodiment1, and those two panels are bonded to each other at a given interval,and liquid crystal is fully inserted between the opposing panels tothereby complete the active matrix liquid-crystal panel.

In this embodiment, a process of manufacturing the liquid-crystal panelwas described with reference to an example of a state in which thethin-film transistors are disposed in the pixel region as shown in FIG.6. Accordingly, the structure of the peripheral drive circuit region(constituted by a shift register, an analog buffer circuit, etc.) fordriving the thin-film transistor in the pixel region in accordance withthis embodiment may be of a structure in which it is formed on the samesubstrate in the same process as that of the thin-film transistor thatforms the pixel region (a structure in which the peripheral drivecircuit and the pixel region are formed on the same substrate), or maybe of a structure in which the peripheral drive circuits constituted byan IC chip is attached externally.

When the formation of the thin-film transistor that constitutes thepixel region and the formation of the thin-film transistor thatconstitutes the peripheral drive circuit region are conducted in thesame process, the thin-film transistor that constitutes the peripheraldrive circuit are simultaneously fabricated together with thefabrication of the thin-film transistor disposed in the pixel regionthrough the same process as that shown in FIG. 5. Also, the thin-filmtransistors that constitute the peripheral drive circuit are aligned inone straight line and so designed that the crystallized region (a regionwhich has been crystallized in a linear form) in accordance with theirradiation of the linear laser beam can be well used.

Fourth Embodiment

A fourth embodiment shows an example in which a quartz glass is usedinstead of the glass substrates shown in the first to third embodiments.When the quartz substrate is used, there arises a drawback that thematerial costs are expensive in comparison with a case in which theglass substrate is used. However, since a high-temperature process of1000° C. or more can be conducted, a crystalline silicon film can beobtained even without using the metal element that promotes thecrystallization of silicon.

In this embodiment, in order to restrain an increase in the costs byusing the quartz substrate, the structure described below is adopted.Even when using the quartz substrate, the liquid-crystal display panelmay be formed through the same process as that in the first and thirdembodiments. In this situation, when the peeling layer made of siliconoxide is etched, the surface of the quartz substrate is also etched witha different extent.

Accordingly, in the present invention, the quartz substrate which hasbeen used once is flattened through the chemical etching or mechanicalpolishing, and grooves are again formed in the surface of the quartzsubstrate, whereby the quartz substrate can be used in plural numbers.

It is assumed that the thickness of the quartz substrate surface to bepolished by one use is about 50 μm, and the quartz substrate having athickness of 2 mm is used. Then, the number of times where the quartzsubstrate can be used until its thickness is reduced to a half isestimated to about 200 times. Under the existing circumstance, since aprice of the quartz substrate with respect to the Corning 7059 glasssubstrate is 10 times in the case of 10 cm², the application of thestructure in accordance with this embodiment can realize the sameproduction costs as that using the glass substrate.

In the case of adopting the structure of this embodiment, theirradiation of a laser beam as shown in FIG. 3 is conducted, to form themonocrystal-like region or substantially monocrystal-like region.Further using this region, the thin-film transistor may be formed. Inthis case, a sample can be heated to about 1000° C., and the effect dueto the irradiation of a laser beam can be enhanced. Also, as shown inthe third embodiment, the effect due to irradiation of a laser beam canbe enhanced using the metal element that promotes the crystallization ofsilicon.

Fifth Embodiment

A fifth embodiment is an example in which a glass substrate is usedinstead of the quartz substrate. When the glass substrate is used, sinceits prices is inexpensive, it can further reduce its production costs incomparison with a case of using a quartz substrate.

Sixth Embodiment

A sixth embodiment is of an example in which a heat treatment isconducted prior to the irradiation of a laser beam in the structureshown in the third embodiment. This heat treatment is conducted so asnot to crystallize the amorphous silicon film to eliminate hydrogen inthe film. After the hydrogen in the film has been eliminated, sincehydrogen that neutralizes dangling bond (unpaired coupling) of siliconnucleus is discharged, the dangling bond (unpaired coupling) of siliconnucleus is increased in the film to lower a threshold value of an energywhen crystallizing. Hence, the crystallization due to the irradiation ofa laser beam can be promoted.

Also, it is effective to apply a heat treatment at a temperature lowerthan a warp point of glass substrate after the irradiation of a laserbeam has been finished. This is because a stress in the film is relaxedthrough the heat treatment.

In particular, as described in the first embodiment, when making aliquid-crystal display panel finally having a flexibility, unless astress in the active layer that constitutes the thin-film transistor issufficiently relaxed, a crack or a defect occurs in the active layer,which adversely affects the operation of the thin-film transistor, by astress applied externally when the liquid-crystal display panel iscurved. Hence, when constituting a flexible liquid-crystal displaypanel, it is largely effective that a heat treatment is conducted afterthe irradiation of a laser beam to relax a stress in the film.

Seventh Embodiment

A seventh embodiment relates to a structure in which a silicon film hasbeen previously crystallized through a heat treatment prior to theirradiation of a laser beam. In other words, the amorphous silicon filmis crystallized by conducting a heat treatment at 550° C. for 4 hoursprior to the irradiation of a laser beam, and a laser beam is furtherirradiated thereon as shown in FIG. 5B, to thereby partially form amonocrystal-like region or substantially monocrystal-like region.

Also, even though the monocrystal-like region or substantiallymonocrystal-like region cannot be formed, the crystalline property whichhas been crystallized by a heat treatment can be further improved by theirradiation of a laser beam.

Eighth Embodiment

An eighth embodiment is of an example in which, in the structuredescribed in the third embodiment, a laser beam is irradiated in a statewhere a condition for irradiating the laser beam is out of an optimumcondition for forming the monocrystal-like region or substantiallymonocrystal-like region. In this case, a region having the crystallineproperty where it is recognized that a slight grain boundary exists canbe obtained. Even though such a region does not provide the electriccharacteristic which can be regarded as the monocrystal-like region, ithas the electric characteristics sufficiently similar to those ofmonocrystal.

The condition which is out of the above-mentioned optimum condition isof a remarkable wide range. Accordingly, the structure shown in thisembodiment is very high in practical use from the viewpoints of thefluctuation of the irradiated power of the laser beam.

Ninth Embodiment

In the present embodiment, a thin-film transistor is manufactured aftergettering nickel within a silicon film which has been crystallizedutilizing nickel element by using a quartz substrate as the substrate tobe peeled off thereby enabling treatment to be conducted at a hightemperature for a long time. Now the present embodiment will bedescribed in the following with reference to FIG. 11.

First, by etching, grid-like or slit-like concave portions are formed onthe surface of a quartz substrate 301, as shown in FIG. 7. The concaveportions are sized to be several thousand Å to several μm in width andin height and several μm to several tens μm in depth.

Next, as shown in FIG. 11 (A), similarly to Embodiment 1, OCD solutionis applied to the surface of the quartz substrate 301 on which theconcave portions are formed, baking is conducted, and a peel-off layer302 which is made of a silicon oxide film and 1 μm thick is formed. Asilicon oxide film as an underlying film 303 which is 5000 Å thick isformed on the surface of the peel-off layer 302 with TEOS gas as thematerial by plasma CVD.

It is important that the hardness of the underlying film 303 should bemade as high as possible. This is because the underlying film 303protects the rear face of the thin-film transistor to be finallyobtained. The harder the underlying film 303 is (that is, the smallerits etching rate is), the higher the reliability of the thin-filmtransistor becomes.

It is effective that the underlying film 303 contains a small amount ofhalogen element represented by chlorine. By doing this, a metal elementwhich exits in the semiconductor layer to promote the crystallization ofsilicon can be gettered by halogen element later in another process.

It is also effective that a hydrogen plasma treatment is additionallyconducted after the underlying film 303 is formed. Also, it is effectiveto conduct a plasma treatment in an atmosphere of mixture of oxygen andhydrogen. This is effective in removing carbon component absorbed in thesurface of the underlying film 303 to improve the interfacialcharacteristics between the underlying film 303 and the semiconductorfilm to be formed later.

Next, an amorphous silicon film 304 which is 2000 Å thick and which isto be a crystalline silicon film later is formed by low pressure thermalCVD or plasma CVD. Low pressure thermal CVD is more preferable, becausethe crystalline silicon film to be obtained later is more minute thanthat obtained by plasma CVD. Since a thermal oxide film is formed lateron the surface of the amorphous silicon film 304, it is necessary tomake the thickness of the amorphous silicon film 304 thicker than thethickness which is finally required.

It is desirable that the amorphous silicon film 304 which ismanufactured here contains oxygen at the concentration of 1×10¹⁷ cm⁻³ to5×10¹⁹ cm⁻³. This is because oxygen plays an important role later in thegettering process of the metal element (metal element which promotescrystallization of silicon). However, it should be noted that, in casethe density of oxygen is higher than the above-mentioned density range,the crystallization of the amorphous silicon film is inhibited. Further,the density of other impurities such as nitrogen and carbon should be aslow as possible. To be concrete, it is necessary that the concentrationshould be 2×10¹⁹ cm⁻³ or less.

As shown in FIG. 11(B), nickel acetate solution containing nickel at adensity of 10 ppm (weight-based) is applied on the surface of theamorphous silicon film 304 and dried to form a nickel layer 305. Thenickel layer 305 does not always form a perfect layer, but the state isalways that nickel element is in contact with the surface of theamorphous silicon film 304. The amount of nickel element to beintroduced is adjusted by adjusting the density of nickel element in thesolution.

Then, a heat treatment is conducted at 900° C. for 4 hours tocrystallize the amorphous silicon film 304 and to obtain a crystallinesilicon film 306 shown in FIG. 11(C). In the present embodiment, sincethe quartz substrate 301 is used, the temperature of heating can beraised up to about 900° C., and thus, the crystalline silicon film 306of higher crystallinity can be obtained in a shorter time compared witha case where a glass substrate is used.

Oxygen will, later in a gettering process, contribute greatly togettering of nickel by combining with nickel. However, it has been foundout that combination of oxygen and nickel in the present step ofcrystallization inhibits the crystallization. Consequently, in thisprocess of crystallization by heating, it is important that formingoxide is restrained as much as possible. Therefore, it is necessary thatthe density of oxygen in the atmosphere where the heating process forcrystallization is conducted should be on the order of ppm, preferably 1ppm or less.

Accordingly, the atmosphere of the heating treatment is nitrogen orinactive gas such as argon.

After the crystalline silicon film 306 is obtained, as shown in FIG.11(D), a heating treatment is again conducted in an atmospherecontaining halogen element to form a thermal oxide film 307. Throughthis process, nickel element which has been intentionally mixed at anearly step for promoting crystallization is removed from within thecrystalline silicon film 306.

The temperature of heating here is higher than that in thecrystallization process. This is an important condition for conductingeffective gettering. In the present embodiment, since the quartzsubstrate 301 is used, the temperature of heating is 950° C. Further,HCl is used as the gas for supplying halogen element, the atmosphere forthe heat treatment is set so that the density of oxygen in the nitrogenatmosphere is 10% and the density of HCl with respect to oxygen (volumedensity) is 3%. Under these conditions, when the time for the treatmentis 300 minutes, a thermal oxide film which is 500 Å thick containingchlorine is formed, and at the same time, by the action of chlorine(halogen element), nickel within the crystalline silicon film 306 isgettered by the thermal oxide film 307 to lower the density of nickel inthe crystalline silicon film 306. The crystalline silicon film 307 isabout 1700 Å thick.

A tendency is observed for the density of nickel element to beheightened around the interface between the crystalline silicon film 306and the thermal oxide film 307. The cause is considered to be that theregion where the gettering is mainly conducted is around the interfacebetween the crystalline silicon film 306 and the thermal oxide film 307on the side of the oxide film. The cause of the proceeding of thegettering around the interface is considered to be the existence ofstress and defect around the interface.

Through this process, the density of nickel element can be lowered to be1/10 or less at the maximum compared with that in an early step. Thismeans that the density of nickel element can be lowered to 1/10 or lesscompared with a case where no gettering by halogen element is conducted.Similar effect can be obtained when other metal elements are used.

The temperature of heating in the gettering process is set so that thedeformation and distortion of the substrate at the temperature areacceptable, and set 500° C. to 1100° C., preferably 700° C. to 1000° C.

For example, when the temperature of heating is 600° C. to 750° C., thetime for the treatment (time for heating) is set 10 hours to 48 hours,representatively 24 hours. When the temperature of heating is 750° C. to900° C., the time for the treatment is set 5 hours to 24 hours,representatively 12 hours. When the temperature of heating is 900° C. to1050° C., the time for the treatment is 1 hour to 12 hours,representatively 6 hours.

The time for the treatment is appropriately set depending on thethickness of the oxide film to be obtained and the density of halogenand oxygen in the atmosphere. For example, in case a heat treatment at950° C. is conducted in an atmosphere where oxygen of 97% and HCl of 3%are contained, in about 30 minutes, a thermal oxide film which is 500 Åthick is formed, and gettering of nickel can not be conducted enough.Consequently, it is necessary in the formation of the thermal oxide filmto adjust the density of halogen and oxygen in the atmosphere in orderto gain enough time for obtaining the effect of the gettering. In otherwords, in case the thickness of the thermal oxide film or thetemperature for the formation is changed, by adjusting the density ofhalogen and oxygen in the atmosphere, time necessary for the getteringcan be set appropriately.

Here, an example is shown where Cl is selected as the halogen elementand HCl is used as the method of introducing Cl. It is preferable thatHCl is mixed at a rate of 0.5% to 10% (vol %) with respect to oxygen. Itshould be noted that if the density of the mixed HCl is higher than theabove-mentioned the surface of the film becomes rough.

Other than HCl, one kind or a plurality of kinds of gases selected fromHF, HBr, Cl₂, F₂, and Br₂ may be used. Generally, halogen hydride may beused. The atmosphere preferably contains these gases at a density of0.25 to 5% in case of HF, 1 to 15% in case of HBr, 0.25 to 5% in case ofCl₂, 0.125 to 2.5% in case of F₂, and 0.5 to 10% in case of Br₂. If thedensity is lower than the above-mentioned range, significant effect cannot be obtained. If the density is higher than the above-mentionedrange, the surface of the silicon film becomes rough.

After the gettering process, as shown in FIG. 11(E), the thermal oxidefilm 307 containing high density of nickel is removed. The thermal oxidefilm 307 is removed by wet etching using buffer hydrofluoric acid (orother etchant of hydrofluoric acid system) or by dry etching. Throughthe etching, a crystalline silicon film 308 with the density of thecontained nickel lowered can be obtained.

Since the density of the contained nickel element is relatively higheraround the surface of the obtained crystalline silicon film 308, it iseffective to make the etching of the oxide film 307 further proceed tooveretch a little the surface of the crystalline silicon film 308.

Finally, as shown in FIG. 11 (F), the crystalline silicon film 308 isetched to be island-like to form an active layer 309 of the thin-filmtransistor. Further, a thermal oxidation treatment is conducted at about900° C. to form a thermal oxide film 310 which is several dozen Å thickon the surface of the active layer 309. Then, using the active layer309, according to the manufacturing process of a thin-film transistor ofEmbodiment 1 shown in FIGS. 2 and 3, a thin-film transistor ismanufactured on the quartz substrate 301, the peel-off layer 301 isremoved by etching, and the thin-film transistor is separated from thequartz substrate 301 to be finally located between a pair of substratesforming a liquid crystal display device.

Since the thermal oxide film 310 is the lowest layer of the gateinsulating film of the thin-film transistor, the energy level of theinterface between the active layer 309 and the gate insulating film maybe lowered than that of the gate insulating film which is deposited byCVD on the interface with the active layer 309, thus enabling the Svalue of the thin-film transistor to be lowered.

As explained in Embodiment 4, since the quartz substrate 301 to bepeeled off may be repeatedly used for about 200 times, employing thequartz substrate 301 does not spoil the economy. Further, since atreatment at a high temperature for a long time is possible by using thequartz substrate 301, nickel can be gettered by a thermal oxide film,and since the lowest layer of the gate insulating film can be formed ofa thermal oxide film, a thin-film transistor with better characteristicscan be manufactured.

Tenth Embodiment

A tenth embodiment is of an applied example in which the liquid-crystaldisplay unit obtained by the present invention described in thisspecification is actually used. What is shown in FIG. 8 is of an examplein which the active matrix liquid-crystal display unit having aflexibility, for example, as described in the first embodiment, isdisposed on a shield (usually constituted by a translucent resinmaterial or a tempered glass) of a helmet used when riding anauto-bicycle. When such a structure is applied, required informationsuch as a speed can be displayed on the shield of the helmet.

When the present invention described in this specification is used,since the liquid-crystal display unit having a flexible property can beobtained, even though, for example, the shape of the helmet isdifferent, its attachment can be readily conducted.

Also, what is shown in FIG. 9 is an example in which the liquid-crystaldisplay unit having a flexible property described in this specificationis attached onto a front portion of a windshield of a vehicle. Also,what is shown in FIG. 10 is an example in which the liquid-crystaldisplay unit having a flexible property described in this specificationis attached onto a front portion of a windshield of an airplane.

As was described above, by using the present invention described in thisspecification, the flexible active matrix liquid-crystal display unitcan be obtained. Also, since the active matrix liquid-crystal displayunit can be formed with the thin-film transistor using ahigh-crystalline silicon thin film, an extremely high displaycharacteristic can be obtained.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiment was chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents.

What is claimed is:
 1. An active matrix flexible display devicecomprising: a first flexible substrate comprising a resin; a circuitincluding a thin film transistor and a pixel electrode electricallyconnected to the thin film transistor wherein the circuit is adhered tothe first flexible substrate through an adhesive; and a second flexiblesubstrate comprising a resin opposed to the first flexible substratewith the circuit interposed therebetween.
 2. The active matrix flexibledisplay device according to claim 1 wherein the pixel electrode islocated between the first flexible substrate and the thin filmtransistor.
 3. The active matrix flexible display device according toclaim 1 wherein the active matrix flexible display device is an ELdisplay.
 4. The active matrix flexible display device according to claim1 wherein the first flexible substrate comprises PET.
 5. The activematrix flexible display device according to claim 1 wherein the adhesivecomprises an epoxy resin.
 6. The active matrix flexible display deviceaccording to claim 1, wherein at least a channel formation region of thethin film transistor contains hydrogen and halogen atoms at a density of1×10²⁰ atoms cm⁻³ or lower, and contains carbon and nitrogen atoms at adensity of 5×10¹⁸ atoms cm⁻³ or lower, and contains oxygen atoms at adensity of 5×10¹⁹ atoms cm⁻³ or lower.
 7. An active matrix flexibledisplay device comprising: a first flexible substrate comprising aresin; a circuit including a thin film transistor and a pixel electrodeelectrically connected to the thin film transistor wherein the circuitis adhered to the first flexible substrate through an adhesive; a secondflexible substrate comprising a resin opposed to the first flexiblesubstrate with the circuit interposed therebetween; and a liquid crystalinterposed between the first flexible substrate and the second flexiblesubstrate wherein the circuit is located between the first flexiblesubstrate and the liquid crystal.
 8. The active matrix flexible displaydevice according to claim 7 wherein the pixel electrode is locatedbetween the first flexible substrate and the thin film transistor. 9.The active matrix flexible display device according to claim 7 whereinthe active matrix flexible display device is an EL display.
 10. Theactive matrix flexible display device according to claim 7 wherein thefirst flexible substrate comprises PET.
 11. The active matrix flexibledisplay device according to claim 7 wherein the adhesive comprises anepoxy resin.
 12. The active matrix flexible display device according toclaim 7 wherein the liquid crystal comprises a resin.
 13. The activematrix flexible display device according to claim 7, wherein at least achannel formation region of the thin film transistor contains hydrogenand halogen atoms at a density of 1×10²⁰ atoms cm⁻³ or lower, andcontains carbon and nitrogen atoms at a density of 5×10¹⁸ atoms cm⁻³ orlower, and contains oxygen atoms at a density of 5×10¹⁹ atoms cm⁻³ orlower.
 14. An article comprising a curved surface and an active matrixflexible display device attached to the curved surface comprising, theactive matrix flexible display device comprising: a first flexiblesubstrate comprising a resin; a circuit including a thin film transistorand a pixel electrode electrically connected to the thin film transistorwherein the circuit is adhered to the first flexible substrate throughan adhesive; and a second flexible substrate comprising a resin opposedto the first flexible substrate with the circuit interposedtherebetween.
 15. The article according to claim 14 wherein the pixelelectrode is located between the first flexible substrate and the thinfilm transistor.
 16. The article according to claim 14 wherein theactive matrix flexible display device is an EL display.
 17. The articleaccording to claim 14 wherein the first flexible substrate comprisesPET.
 18. The article according to claim 14 wherein the adhesivecomprises an epoxy resin.
 19. The article according to claim 14 whereinthe article is a vehicle.
 20. The article according to claim 14, whereinat least a channel formation region of the thin film transistor containshydrogen and halogen atoms at a density of 1×10²⁰ atoms cm⁻³ or lower,and contains carbon and nitrogen atoms at a density of 5×10¹⁸ atoms cm⁻³or lower, and contains oxygen atoms at a density of 5×10¹⁹ atoms cm⁻³ orlower.
 21. An article comprising a curved surface and an active matrixflexible display device attached to the curved surface comprising, theactive matrix flexible display device comprising: a first flexiblesubstrate comprising a resin; a circuit including a thin film transistorand a pixel electrode electrically connected to the thin film transistorwherein the circuit is adhered to the first flexible substrate throughan adhesive; a second flexible substrate comprising a resin opposed tothe first flexible substrate with the circuit interposed therebetween;and a liquid crystal interposed between the first flexible substrate andthe second flexible substrate wherein the circuit is located between thefirst flexible substrate and the liquid crystal.
 22. The articleaccording to claim 21 wherein the pixel electrode is located between thefirst flexible substrate and the thin film transistor.
 23. The articleaccording to claim 21 wherein the active matrix flexible display deviceis an EL display.
 24. The article according to claim 21 wherein thefirst flexible substrate comprises PET.
 25. The article according toclaim 21 wherein the adhesive comprises an epoxy resin.
 26. The articleaccording to claim 21 wherein the liquid crystal comprises a resin. 27.The article according to claim 21 wherein the article is a vehicle. 28.The article according to claim 21, wherein at least a channel formationregion of the thin film transistor contains hydrogen and halogen atomsat a density of 1×10²⁰ atoms cm⁻³ or lower, and contains carbon andnitrogen atoms at a density of 5×10¹⁸ atoms cm⁻³ or lower, and containsoxygen atoms at a density of 5×10¹⁹ atoms cm⁻³ or lower.